UN Secretary-General Ban Ki-moon has called on the Security Council to refer the situation in Syria to the International Criminal Court for investigation of possible war crimes.

Mr Ban said he was "deeply disappointed" at the lack of unity on Syria in the council, demonstrated by Russia's veto on Saturday of a Western-backed resolution demanding an immediate bombing halt.

Mr Ban said the council must stop debating and disagreeing and "work to protect human lives, to bring this matter to a political solution".

For this to happen, he again urged a ceasefire "to build trust and confidence among the parties" and an immediate bombing halt in Aleppo and elsewhere.

Mr Ban's comments followed a call from France's foreign minister for the ICC to investigate Russia for possible war crimes in Syria.

Jean-Marc Ayrault said: "France intends to get in touch with the prosecutor to find out how the probe can be launched."

Mr Ayrault said France disagrees with Russia's "bombarding" of Aleppo and "is committed as never before to saving the population".

He said the investigation would hinge on Moscow's role in the aerial offensive in the rebel-held eastern part of the city.

Meanwhile, Doctors Without Borders have pleaded for access to treat the wounded in the rebel-held part of Aleppo, as Syrian government forces pressed ahead with an offensive that has killed hundreds of people in recent weeks.

The international charity, also known by its French acronym MSF, said medical workers in Aleppo are exhausted and the overstretched facilities face an impending fuel shortage.

MSF, which supports eight hospitals in Aleppo's besieged eastern quarters, said just 35 doctors remain in the area, serving a population of 275,000.

The UN has warned that the Aleppo bombardment by Syrian and Russian war planes could leave thousands more dead by the end of the year.

"Russia and Syria must stop the indiscriminate bombing now and abide by the rules of war to avoid the extreme suffering of the unprotected civilian population," said Pablo Marco, MSF's operations manager for the Middle East.

The Britain-based Syrian Observatory for Human Rights, which monitors the conflict through local contacts, reported heavy fighting along the east-west Aleppo front lines.

Another activist-run group, the Local Coordination Committees, said rebels were fighting to repel government forces from the city's largest water facility, which serves more than a million people.

In another besieged area near the capital, Damascus, doctors reported up to two dozen cases of kidney failure that they said resulted from malnutrition. Muhammad Darwish, a local physician, said doctors confirmed renal failure in 12 people in the town of Madaya and were investigating another 12 cases.

Government forces have laid siege to Madaya, home to some 40,000 people, since late last year. Last winter, MSF reported at least 16 deaths there resulting from malnutrition and lack of medical care.

"We are only eating carbohydrates. We aren't receiving any vitamins or protein," said Mr Darwish.

The government has prohibited the UN from delivering seeds or dialysis kits to the town, in what the opposition says is a strategy aimed at forcing the town to surrender.